The invention relates to a stereolithography apparatus and method of controlling light in a stereolithography apparatus.
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Additive manufacturing (AM), commonly known as three-dimensional (3D) printing, has been a fast developing area for more than three decades. It is a process that uses information from a computer-aided design file to build a 3D physical object. It has significant advantages over traditional manufacturing methods in (1) rapid creation of 3D prototypes, and (2) cost-effective production of patterns and molds with complex surfaces. Many materials have already been used in additive manufacturing such as polymer, metal, and ceramic. There are several technologies that have been developed for additive manufacturing, including stereolithography, binder printing (3DP), fused deposition modeling, selective laser sintering (SLS), etc. Among these technologies, stereolithography is the first commercially available prototyping machine and one of the most widely used AM processes.
The production efficiency of stereolithography is determined by many factors, such as light spot diameter, scanning speed, hatch space, and curing depth. Among them, light spot diameter is the most direct way to determine the production efficiency.
The diameter of the light spot is determined by the entire optical system and could be difficult to control precisely. Therefore, most stereolithography systems set the spot diameter as a constant. The specific value is a tradeoff between the size of the part that is being built and the desired resolution, which is typically about 0.1%-0.5% of the overall dimension. For this reason, a variable beam spot that can improve production efficiency while keeping high resolution is a promising direction for stereolithography. With a variable beam spot, a large spot can fill an open area quickly and a small spot can build details that require high resolution. Many studies have been carried out on methods to change spot size. Miller et al. developed a SLS workstation that has two laser spot sizes by pulling an aperture into and out of light path. Sim et al. used lenses with different focal length to produce different laser spot sizes. Cao et al. reported a stereolithography process that uses a dynamic focusing mirror to change spot size. Several specimens demonstrated more than 25% building time saving.
Most of the studies involved the dynamic motion of optical components such as lens or physical aperture. Hence, cost of the systems would be increased due to the requirement of precise control of the motion during the fabrication process.